The present invention relates to a contoured tank liner and a method of production of such a liner, and more particularly, it relates to such tank liner and method of production where the base of the tank liner presents a substantially flat surface of approximately circular configuration when the liner is disposed in a tank and contains a fluid. The tank liners of the invention are particularly useful for mixing biologics, since they may be sterilized.
Tank liners are well known in the art and are used in many applications. Generally speaking, tank liners are used for lining tanks in which a fluid is disposed and where it is desired that the fluid not contaminate the tank. For example, if a biologic liquid, such as blood, plasma, etc., or a saline solution, which for present purposes is considered as a biologic liquid, is processed in a tank without a liner, after that liquid has been processed and discharged from the tank, the tank must be thoroughly cleaned, under biological standards, before that tank can be reused for processing a further batch of the liquid. However, when a tank liner is used in such a tank, and when that tank liner has been previously sterilized, the liquid can be processed within the tank and tank liner, and after a discharge of the liquid, the tank liner is simply disposed of and a new sterilized tank liner is placed into the tank for subsequent processing of additional liquid.
Thus, tank liners are used in applications where it is less expensive to use a tank liner and avoid the necessary thorough cleaning of the tank, as well as the extensive biological and analytical studies required to prove to regulatory agencies that the tank is clean. As can therefore be easily appreciated, in view of that economic consideration, in order for such disposable tank liner to be commercially acceptable, it must be manufactured at a relatively low cost. Otherwise, it would be more economical to clean the tank after each use.
Accordingly, prior art tank liners, in order to be manufactured at a low cost, are, generally, relatively uncomplicated structures, so as to promote ease of manufacture and, hence, production at a low cost. Typically, such disposable tank liners are made from tubular thermoplastic film.
In one prior art liner, a weld seam is made transverse to the longitudinal direction of the tubular film to form a closed bottom of the film and produce a liner. However, when such liners are disposed in a conventional processing tank, which typically is generally cylindrical and has a generally flat bottom, the welded base bunches against the flat bottom of the tank when the liner contains a fluid, and the base, thus presented, is not flat but exceedingly rough. This rough base causes difficulties in processing and especially in mixing, and most especially in mixing biologics, since it is necessary, for example, that a solid solute be completely dissolved in a solvent to ensure that the concentration of the solute in the solvent is as required. With the rough bottom of such conventional tank liners, as described above, for example, solid solute, such as a saline solute, can settle to the bottom of the liner disposed in the tank before being solubilized, and the rough surface on the base of the liner tends to trap that undissolved solute and prevent that solute from being solubilized by the solvent. When this occurs, either prolonged mixing is required, which is uneconomical, or the solution will not have the desired concentration of solubilized solute therein and is, generally, therefore not acceptable for use.
In addition, the conventional tank liner, as described above, when disposed in a generally cylindrical tank and containing a liquid, not only presents the rough base, due to bunching of the liner at the base, but, in addition, bunches around the side walls of the tank near its base because the base of the liner, being simply welded along its traverse, cannot form a configuration in the tank which approximates a circular configuration of a generally cylindrical tank. This bunching of the liner at the side walls near the base, again, causes a rough surface against which, for example, the solvent must flow during mixing. That rough surface can produce stagnant pockets of the solvent, which can result in inadequate mixing of the solute in the solvent and can produce variations in the concentration of the solute throughout the bulk of the solution. If, for example, the solution is removed from the tank and serially loaded into separate containers, for example, sterile saline bags, then it is possible that the concentration of the solute in those serially filled saline bags will be different, which is quite unacceptable.
In another prior art liner, efforts have been made to avoid the above-described difficulties. This other prior art liner uses, again, a tubular thermoplastic film, but seam welds to an end thereof a circular disc so as to provide a circular bottom to the tank liner. Basically, the disc has a greater diameter than the diameter of the tubular film. A lower edge of the tubular film is bent inwardly to form an inwardly directed xe2x80x9cflangexe2x80x9d and the disc, with edges extending over the flange and beyond the diameter of the tubular film, is welded, along its circumference, thereto.
However, this approach has a number of disadvantages. Aside from the high cost of tooling and difficulty of manufacture, the inwardly bent flange remains along the inside circumference of the bottom of the finished liner and presents not only a rough surface, as described above, but also presents areas along the circumference which can, for example, trap solute during mixing.
Further, the thermoplastic of choice of the tank liner is a polyolefin, e.g. polyethylene, since that thermoplastic has excellent welding properties. Thus, to make the circular weld, described above, the weld must be between polyolefin surfaces, which means that an outside surface of the liner cannot have a barrier layer film thereon. Normally, tank liners for processing biologics have a polyolefin film bonded to an outside barrier layer film, e.g. a nylon film. This is because polyolefins are permeable, which is most undesirable for biologics since tank contamination can occur. Thus, an impermeable barrier layer film, e.g. nylon film, is required as an outside layer of the thermoplastic film for most biologics processing liners. This nylon outside barrier layer film also greatly increases tear resistance of the liner.
Also, in both of the above-described prior art approaches using tubular thermoplastic film, the diameter, and hence size, of the tank liner is dictated by commercially available diameters of tubular film. This means that the liners cannot be manufactured to snugly fit all usual tanks.
Thus, neither of these prior art tank liners is fully acceptable and, hence, have not been widely used.
As a result of the foregoing, when critical processing is required, e.g. mixing of a solute in a solvent, in biologics, it is not uncommon for manufacturers to dispense with the use of a tank liner, because of the above-described difficulties, and accept the increased cost of production associated with a thorough cleaning and inspection of a tank, accordingly to biologic standards, after each use.
From the above, it can easily be seen that it would be a substantial advantage in the art to provide a disposable tank liner, where the base presents a substantially flat surface, so as to avoid the rough base surface of the prior art and the possibility of difficulties, as described above. It would also be a substantial advantage in the art to provide such a liner with a base which approximates a circular configuration when the liner is disposed in the tank and contains a liquid, so as to avoid the bunching of the liner at the side walls near the base, and the difficulties associated therewith, as described above.
It would also be an advantage to provide such liner which can be made of thermoplastic film having a barrier layer film on all parts thereof and one which does not have a circumferential flange which can trap solute.
The present invention is based on several primary and subsidiary discoveries.
As a first primary discovery, it was found that it is possible to provide a base for a disposable tank liner, which presents both a substantially flat base surface and one of approximately a circular configuration when the liner is disposed in a generally cylindrical tank and contains a liquid. This is achieved when the base is constructed with six angular flaps depending from side walls of the liner and those flaps are at least in part, joined together by seams. This construction provides a base in a generally hexagon configuration, which will fairly closely approximate a circular configuration when the liner is disposed in a generally cylindrical tank and contains a liquid. This approximate circular configuration avoids bunching of the liner on the side walls of the tank near the base thereof and, likewise, avoids the difficulty of the prior art liners, as described above in that connection.
As a second primary discovery, it was found that when the base is so formed with the six flaps, the liner can be provided with a base having a substantially flat surface, and this avoids the difficulty of the bunched liner base, as described above in connection with conventional liners.
As a third primary discovery, it was found that, with this construction of the base, the liners can be produced at a very low cost and are therefore economically acceptable for disposable use, as opposed to thorough cleaning of a tank after each use thereof, as explained above.
As a subsidiary discovery, it was found that the six angular flaps must have seams between specific of those flaps in order to provide the substantially flat surface and approximately circular configuration.
As another subsidiary discovery, it was found that the present construction of the base, as described above, is applicable to a variety of configurations of the thermoplastic film from which the liner is constructed, therefore making the manufacture of the liner quite convenient and versatile. The liner may be made of a single piece of flat thermoplastic film, or the liner may be made of two superimposed films, or the liner may be made of a single piece of tubular film.
It will also be appreciated from the above that it is potentially possible to form a somewhat flat and somewhat circular configured base with less than six flaps or more than six flaps, but it was found, as a subsidiary discovery, that constructing the base with only four flaps does not sufficiently prevent the bunching of the liner in the tank, as described above, and that eight or more flaps so considerably complicate the construction of the liner that the liner is no longer economical to produce. As a subsidiary discovery in this regard, it was also found that the flaps must be an even number, so that one set of the flaps is formed on one side wall of the liner and another set of the flaps is formed on an opposite side wall of the liner and so that, with such even number of flaps, half of which is disposed on one side wall and half of which is disposed on the opposite side wall, the constructed liner will achieve the approximately circular configuration and flat surface of the base and with an acceptable cost.
Thus, briefly stated, the present invention is an improvement in a thermoplastic film tank liner which, when disposed within a generally cylindrical tank and containing a liquid, has a generally cylindrical configuration. The tank liner has an opened top, side walls and a closed base. The improvement of the invention is wherein the base comprises a first and a second flap extending from lower portions of a first side wall and having, respectively, first and second angular edges. A third and a fourth flap extend from lower portions of an opposite side wall and have, respectively, third and fourth angular edges. A first intermediate flap and a second intermediate flap extend, respectively, from lower portions of the first and opposite side walls and are positioned, respectively, between the first and second flaps and the third and fourth flaps. Each of the intermediate flaps has transition portions joined together and, respectively, first left and first right angular edges and opposite left and opposite right angular edges. A seam is disposed between: (a) the first angular edge and the first left angular edge; (b) the second angular edge and the first right angular edge; (c) the third angular edge and the opposite left angular edge; and (d) the fourth angular edge and the opposite right angular edge. All of the angular edges have angles such that the base presents a substantially flat surface of approximately a circular configuration when the liner is disposed in a tank and contains a liquid.
The invention also provides a method for producing the above-described tank liner. The method comprises cutting from at least one thermoplastic film a first flap and a second flap which extend from lower portions of a first side wall and having, respectively, a first angular edge and second angular edge; cutting from the at least one thermoplastic film a third flap and a fourth flap which extend from lower portions of an opposite side wall and having, respectively, a third angular edge and a fourth angular edge; said cutting being such that a first intermediate flap and a second intermediate flap extend, respectively, from the lower portions of the first side wall and the opposite side wall and are positioned, respectively, between the first flap and second flap and the third flap and fourth flap, and wherein each intermediate flap has transverse portions joinable together and has, respectively, a first left angular edge and a first right angular edge and an opposite left angular edge and an opposite right angular edge; forming a seam between: (a) the first angular edge and the first left angular edge; (b) the second angular edge and the first right angular edge; (c) the third angular edge and the opposite left angular edge; and (d) the fourth angular edge and the opposite right angular edge; and wherein said cutting is such that all of said angular edges have angles such that the base presents a substantially flat surface of approximately a circular configuration when the liner is disposed in said tank and contains a liquid.
Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.